MAGNETIC-RESONANCE FLUOROSCOPY USING SPIRALS WITH VARIABLE SAMPLING DENSITIES

The imaging of dynamic processes in the body is of considerable intere st in interventional examinations as well as kinematic studies, and sp iral imaging is a fast magnetic resonance imaging technique ideally su ited for such fluoroscopic applications, In this manuscript, magnetic resonance fluoroscopy pulse sequences in which interleaved spirals are used to continuously acquire data and reconstruct one movie frame for each repetition time interval are implemented. For many applications, not all of k-space needs to be updated each frame, and nonuniform k-s pace sampling can be used to exploit this rapid imaging strategy by al lowing variable update rates for different spatial frequencies, Using the appropriate reconstruction algorithm, the temporal updating rate f or each spatial frequency is effectively proportional to the correspon ding k-space sampling density, Results from a motion phantom as well a s in in vivo gadolinium diethylenetriaminopentaacetic acid (Gd-DTPA) b olus tracking studies in a rat model demonstrate the high temporal res olution achievable using these techniques as well as the tradeoffs ava ilable with nonuniform sampling densities, This paper focuses on the a cquisition of real-time dynamic information, and all images presented are reconstructed retrospectively. The issues of real-time data recons truction and display are not addressed.